Types Of Saccades Research Articles

Saccadic movements during reading of text in children and university professors considered good readers

The present study evaluated 4-grade children and university professors considered good readers in a computerized test of textreading. Trajectories of eye movements obtained during reading made possible to compare the two groups regarding the number of regressivesaccades; type of regressive saccade - that could be intra-word or inter-word; and grammatical classification of words that suffered regression.Results show that children presented a higher number of regressive saccades than university professors. Both groups carried out more inter-wordregressions to the word immediately antecedent to the last fixation than intra-word regressions. The two groups carried out more intra-wordsregressive saccades in the following word types: nouns, adjectives and verbs. Regressions to the previous word took place principally in wordcouples conjunction-verb, adjective-noun, and preposition-noun. On the whole, good readers carry out fewer regressive saccades than childrenin the process of literacy, but the standard of regressive saccades and the type of words that suffer regression are similar in the two groups.Also a higher number of regressive saccades was observed in the beginning of each line of the text, which can be explained by paraphovealprocessing in reading. Regressions to the previous word may be related to the fact that, depending on the grammatical class of the word, thereis a higher possibility of its not fixed.

White matter connections reflect changes in voluntary-guided saccades in pre-symptomatic Huntington's disease

Huntington's disease is caused by a known genetic mutation and so potentially can be diagnosed many years before the onset of symptoms. Neuropathological changes have been found in both striatum and frontal cortex in the pre-symptomatic stage. Disruption of cortico-striatal white matter fibre tracts is therefore likely to contribute to the first clinical signs of the disease. We analysed diffusion tensor MR image (DTI) data from 25 pre-symptomatic gene carriers (PSCs) and 20 matched controls using a multivariate support vector machine to identify patterns of changes in fractional anisotropy (FA). In addition, we performed probabilistic fibre tracking to detect changes in 'streamlines' connecting frontal cortex to striatum. We found a pattern of structural brain changes that includes putamen bilaterally as well as anterior parts of the corpus callosum. This pattern was sufficiently specific to enable us to correctly classify 82% of scans as coming from a PSC or control subject. Fibre tracking revealed a reduction of frontal cortico-fugal streamlines reaching the body of the caudate in PSCs compared to controls. In the left hemispheres of PSCs we found a negative correlation between years to estimated disease onset and streamlines from frontal cortex to body of caudate. A large proportion of the fibres to the caudate body originate from the frontal eye fields, which play an important role in the control of voluntary saccades. This type of saccade is specifically impaired in PSCs and is an early clinical sign of motor abnormalities. A correlation analysis in 14 PSCs revealed that subjects with greater impairment of voluntary-guided saccades had fewer fibre tracking streamlines connecting the frontal cortex and caudate body. Our findings suggest a specific patho-physiological basis for these symptoms by indicating selective vulnerability of the associated white matter tracts.

Adaptation of Voluntary Saccades, But Not of Reactive Saccades, Transfers to Hand Pointing Movements

Studying the transfer of visuomotor adaptation from a given effector (e.g., the eye) to another (e.g., the hand) allows us to question whether sensorimotor processes influenced by adaptation are common to both effector control systems and thus to address the level where adaptation takes place. Previous studies have shown only very weak transfer of the amplitude adaptation of reactive saccades--i.e., produced automatically in response to the sudden appearance of visual targets--to hand pointing movements. Here we compared the amplitude of hand pointing movements recorded before and after adaptation of either reactive or voluntary saccades, produced either in a saccade sequence task or in a single saccade task. No transfer to hand pointing movements was found after adaptation of reactive saccades. In contrast, a substantial transfer to the hand was obtained following adaptation of voluntary saccades produced in sequence. Large amounts of transfer between the two saccade types were also found. These results demonstrate that the visuomotor processes influenced by saccadic adaptation depend on the type of saccades and that, in the case of voluntary saccades, they are shared by hand pointing movements. Implications for the neurophysiological substrates of the adaptation of reactive and voluntary saccades are discussed.

Saccadic Ping Pong Gaze in Coma

In this report, we describe the peculiar eye movements of a young man who became comatose after a head injury. The eyes moved rhythmically from one side to another, without pausing in the lateral positions. This phenomenon has been described as "ping pong gaze" (PPG), referring to short-cycling periodic alternating gaze with smooth eye deviations. In the present patient, however, a saccadic type of PPG could be confirmed by oculography. Possible clinical and pathophysiological implications are discussed.

Saccade landing point selection and the competition account of pro‐ and antisaccade generation: The involvement of visual attention – A review

This paper presents a review and summary of experimental findings on the role of attention in the preparation of saccadic eye movements. The focus is on experiments where performance of prosaccades (saccades towards a suddenly appearing item) and antisaccades (saccades of equal amplitude in the direction opposite to where the target moved) is compared. Evidence suggests that these two opposite responses to the same stimulus event entail competition between neural pathways that generate reflexive movements to the target and neural mechanisms involved in inhibiting the reflex and generating a voluntary gaze shift in the opposite direction to the target appearance. Evidence for such a competition account is discussed in light of a large amount of experimental findings and the overall picture clearly indicates that this competition account has great explanatory power when data on saccadic reaction times and error rates are compared for the two types of saccade. The role of attention is also discussed in particular in light of the finding that the withdrawal of attention by a secondary task 200 to 500 ms before the saccade target appears, leads to speeded antisaccades (without a similar increase in error rates), showing that the results do not simply reflect a speed-accuracy trade-off. This result indicates that the tendency for "reflexive" prosaccades is diminished when attention is engaged in a different task. Furthermore, experiments are discussed that show that as the tendency for a reflexive prosaccade is weakened, antisaccades are speeded up, further supporting the competition account of pro- and antisaccade generation. In the light of evidence from neurophysiology of monkeys and humans, a tentative model of pro- and antisaccade generation is proposed.

When does action resist visual illusion? The effect of Müller–Lyer stimuli on reflexive and voluntary saccades

The primate visual cortex exhibits two anatomically distinct pathways (dorsal and ventral). According to the "two visual systems hypothesis" (TVSH) of Milner and Goodale (The visual brain in action. Oxford University Press, Oxford, 1995), this anatomical distinction corresponds to a functional division of labor between vision-for-action (dorsal) and vision-for-perception (ventral). This proposal is supported by evidence that, in healthy volunteers, perceptual responses are affected by visual illusions, whereas motor responses to the same illusion-inducing stimuli are not. However, previously we have shown that the amplitude of saccadic eye movements is modified by the Müller-Lyer illusion in a similar manner as perceptual responses. Here we extend this finding to reflexive and voluntary (memory-guided) saccades. We show that both types of saccade can be strongly affected by the illusion. In our studies, the effect on reflexive saccades was comparable to that usually observed with verbal reports (an effect size of 22 +/- 8%), whereas the effect on voluntary saccades was smaller (11 +/- 11%). In addition, both types of saccade provide evidence for the scaling bias usually observed in perceptual responses. We suggest that previous studies may have employed methods that generally reduced the effect of the illusion. Interpretations of dissociations between reflexive and voluntary saccades in terms of the TVSH appear to be premature.

Oculomotor plasticity: Are mechanisms of adaptation for reactive and voluntary saccades separate?

Saccadic eye movements are permanently controlled and their accuracy maintained by adaptive mechanisms that compensate for physiological or pathological perturbations. In contrast to the adaptation of reactive saccades (RS) which are automatically triggered by the sudden appearance of a single target, little is known about the adaptation of voluntary saccades which allow us to intentionally scan our environment in nearly all our daily activities. In this study, we addressed this issue in human subjects by determining the properties of adaptation of scanning voluntary saccades (SVS) and comparing these features to those of RS. We also tested the reciprocal transfers of adaptation between the two saccade types. Our results revealed that SVS and RS adaptations disclosed similar adaptation fields, time course and recovery levels, with only a slightly lower after-effect for SVS. Moreover, RS and SVS main sequences both remained unaffected after adaptation. Finally and quite unexpectedly, the pattern of adaptation transfers was asymmetrical, with a much stronger transfer from SVS to RS (79%) than in the reverse direction (22%). These data demonstrate that adaptations of RS and SVS share several behavioural properties but at the same time rely on partially distinct processes. Based on these findings, it is proposed that adaptations of RS and SVS may involve a neural network including both a common site and two separate sites specifically recruited for each saccade type.

Role of the calcarine cortex (V1) in perception of visual cues for saccades

Objective To determine the initial level at which the pathways for cue perception, saccades and antisaccades diverge. Methods Two procedures: single pulse transcranial magnetic stimulation (sTMS) over posterior occiput and backward masking were used. A visual cue directed saccades to the left or right, either a pro-saccade (to the side of the cue but beyond it) or an antisaccade, i.e., contraversive saccade. No visual target was presented. Results Latencies of the two types of saccades did not differ. Focal sTMS applied unilaterally over V1 suppressed both perception of a cue flashed 80–90 ms earlier contralaterally (but not ipsilaterally) and the appropriate saccade. Masking at a delay of 100 ms abolished the appropriate saccade and cue perception. Conclusions V1 is essential for the perception of a flashed cue and for executing appropriate pro- and contraversive saccades. Masking may occur beyond V1, where the pathways for perception and for saccades at least to the next visual processing level start separating. Significance VI is needed for rapid, accurate perceptual and motor responses to the crudest (left versus right) cues. It is unlikely that the “where” system can have a major direct input bypassing V1.

Saccadic trajectory in Huntington's disease

Trajectories of saccadic eye movements can be modulated by the presence of a competing visual distractor. It is proposed that the superior colliculus (SC) controls the initial deviation through competitive lateral interactions. Given the ramifications of connections between basal ganglia (BG) thalamo-cortical circuitry and the SC, it was anticipated that this modulation would be differentially effected in those with Huntington's disease, which in its early stages is primarily a disorder of the BG. Horizontal deviation was determined for exogenously driven and endogenously driven vertical saccades in the presence of peripheral distractors. For neurologically healthy participants, the initial trajectories of both saccade types curved away from distractor locations, as predicted. However, for HD participants exogenous saccades consistently deviated leftwards, irrespective of distractor location. Endogenous saccades also revealed anomalous horizontal deviation, with significant leftward deviation evident for saccades directed upward and significant rightward deviation for saccades directed downward. Further, both groups generated a comparable proportion of erroneous responses to distractor stimuli, but only neurologically healthy participants demonstrated a response time advantage for compatible target/distractor presentation. These results suggest anomalous regulation of distractor-related activity in HD.

Eye movement signals influence perception: Evidence from the adaptation of reactive and volitional saccades

Information about upcoming saccadic eye movements is used to orient visuo-spatial attention across the visual field. Different eye movement signals (intended or actual) could be used according to the intentionality of the saccade in preparation (Reactive or Volitional), and can be dissociated by saccadic adaptation. Gap 0 and overlap paradigms were contrasted to elicit the two saccade populations with different latencies and an asymmetric transfer of saccadic adaptation. Preparation of both saccade types caused a concomitant shift in the attentional focus (indexed by relative perceptual performance) to the actual, not intended, eye position. The attentional shift emerged progressively, earlier for V-saccades but reaching a maximal level around saccade onset for both saccade types. These results suggest that information about actual eye movements mediates the pre-saccadic shift of attention.

The inter-trial effects of stimulus and saccadic direction on prosaccades and antisaccades, in controls and schizophrenia patients

We investigated the influence of the direction of preceding saccadic trials on the latency of current prosaccades and antisaccades, in healthy subjects and patients with schizophrenia. When prosaccades and antisaccades were performed in separate, single-task blocks, we found that only prosaccades were delayed if the saccade in the prior trial was in the same direction, consistent with the expected directional effect from an 'inhibition of return'-like alternation advantage. However, both types of saccades were executed more quickly when the saccade in the penultimate trial was in the same direction, consistent with previous demonstrations of directional plasticity in monkeys. In blocks of randomly mixed prosaccades and antisaccades, the directional effects in healthy subjects were greatest when a prosaccade was preceded by an antisaccade, consistent with a summation of effects of alternation advantage (from the prior stimulus) and directional plasticity (from the prior saccade). Schizophrenic patients showed an additional phenomenon, a directionally specific inhibition of upcoming saccades by preceding antisaccades. These results suggest that saccades in humans are modulated by inter-trial effects attributable to both an 'inhibition of return'-like alternation advantage and directional plasticity.

The control of vertical saccades in aged subjects

In real life we produce vertical saccades at different distances and eccentricities, and while our fixation is more or less actively engaged. The goal of this study is to examine vertical saccades in aged and young subjects, taking into consideration all these parameters. Eleven adults (20-28 years) and 11 aged subjects (63-83 years) were recruited. We used LED targets at 7.5 degrees or 15 degrees, up or down in four conditions: gap and overlap tasks, each done at two distances-at near (40 cm) and at far (150 cm). In the gap task fixation target extinguishes prior to target onset, while in the overlap condition it stays on after target onset; consequently, visual attention and fixation are employed differently in the two tasks. Eye movements were recorded with the Chronos video eye tracker. Results showed that vertical saccades were longer for aged subjects than for young adults under almost all conditions. For both aged and young subjects, latencies were shorter under the gap than under the overlap task. Latencies for eccentric targets at 15 degrees were significantly longer than those at 7.5 degrees but for aged subjects only; this effect was more pronounced for upward saccades under the overlap condition. Express type of latencies (80-120 ms) occurred frequently in the gap task and at similar rates for young adults (16%) and aged subjects (12%); in the overlap task express latencies were scarce in young adults (0.4%) and aged subjects (1.8%). Age deteriorates the ability to trigger regular volitional saccades but not the ability to produce express type of saccades. Latency increase with aging is attributed to the degeneration of central areas, e.g. oculomotor cortical areas involved in the initiation of vertical saccades.

Shared decision signal explains performance and timing of pursuit and saccadic eye movements

Each voluntary eye movement provides physical evidence of a visuomotor choice about where and when to look. Primates choose visual targets with two types of voluntary eye movements, pursuit and saccades, although the exact mechanism underlying their coordination remains unknown. Are pursuit and saccades guided by the same decision signal? The present study compares pursuit and saccadic choices using techniques borrowed from psychophysics and models of response time. Human observers performed a luminance discrimination task and indicated their choices with eye movements. Because the stimuli moved horizontally and were offset vertically, subjects' tracking responses consisted of combinations of both pursuit and saccadic eye movements. For each of two signal strengths, we constructed speed-accuracy curves for pursuit and saccades. We found that speed-accuracy curves for pursuit and saccades have the same shape, but are time-shifted with respect to one another. We argue that this pattern occurs because pursuit and saccades share a decision signal, but utilize different response thresholds and are subject to different motor processing delays.

Effects of switching between leftward and rightward pro- and antisaccades

Previous studies suggested that random switching between pro- and antisaccades increases errors in both tasks. However, little is known about the effects of switching between leftward and rightward saccades (response switching). The present study investigated task and response switching using an alternating runs procedure. Tasks (i.e., prosaccades versus antisaccades) were switched every second trial. Response switches (i.e., leftward saccades versus rightward saccades) were counterbalanced across tasks and task-switching conditions. Task switching increased errors in both tasks. Response switching increased errors when antisaccades were preceded by antisaccades but not when antisaccades were preceded by prosaccades or for prosaccades regardless of the preceding saccade type. The task-switch effects suggest that both pro- and antisaccade trials activate specific production rules that can persist in a subsequent trial. The differential response-switch effects may reflect different modes of response activation in pro- and antisaccades (sensorimotor transformation of visual information versus selection of motor programs).

Developmental fractionation and differential discrimination of the anti-saccadic direction error

This partial re-analysis of the data of a total of 433 experimental sessions transfers the distinction of "express" and "regular" latency ranges from the pro-saccade task to the latencies of the anti-saccadic direction errors. Express errors and express saccades (ES) loaded on one and the same PCA factor, and both variables were subject to only minor developmental changes from childhood to young adulthood. Regular direction errors loaded, with opposite signs, on the same factor as pro-saccadic reaction times and were unrelated to express errors; these direction errors showed substantial developmental changes. Our data contribute with new evidence from the anti-saccade task to the long standing debate on whether ES should be considered as a separate type of saccade. Anti-saccadic direction errors with express latencies can be distinguished from those with regular latencies. Future anti-saccade task research should therefore analyse these error types separately in order to look for further evidence in favour of their conceptual and statistical distinction.

The effect of transcranial magnetic stimulation on the latencies of vertical saccades

In this study, we investigated the effect of transcranial magnetic stimulation (TMS) over the right posterior parietal cortex (PPC) on the latency of two different types of visually-guided vertical saccades: reflexive saccades triggered by the sudden onset of a target, and saccades towards target locations known in advance. For this reason, we used two oculomotor tasks: a gap and a delay task, respectively. Nine normal subjects performed vertical saccades at +/-7.5 and +/-15 degrees . TMS was applied at 80 and 100 ms after target onset in the gap task, and after fixation offset in the delay task. Without TMS, we confirmed a latency asymmetry in the gap task favouring upward saccades at the lower eccentricity (7.5 degrees ), and a latency symmetry in the delay task. TMS increased the latencies of all saccades in the delay task, when delivered at 100 ms. This effect was mostly pronounced for downward saccades at 7.5 degrees . As a result, saccade latencies showed an asymmetry in this condition, similar to the one observed in the gap task without TMS. The gap task with TMS resulted in a variable latency distribution and no significant overall effect on saccade latency. Our results indicate that the right PPC is involved in the initiation of vertical saccades in the delay task, and that this involvement appears to be enhanced for downward saccades. A conclusion for the involvement of this area in the gap task could not be drawn from this study.

Specific Deficits of Saccadic Eye Movements after Sleep Deprivation

Sleep deprivation (SD) and reduced vigilance impair not only the performance of cognitive tasks, but also of saccadic eye movements. Previous literature reports reduced peak velocities and prolonged latencies of visually-guided saccades, but the latter remained controversial. To clarify which specific saccadic subfunctions reflect reduced vigilance, we investigated the effect of a one-night SD on 3 different types of saccades that are controlled by different cortical networks: 1) visually-guided pro-saccades controlled more by the parietal (PEF) than by the frontal eye field (FEF; 2) anti-saccades (performed into the direction opposite to a peripheral target, with respect to the vertical meridian), controlled by FEF, the dorsolateral prefrontal cortex (DLPFC), and the basal ganglia loop; 3) memory-guided saccades (performed to a peripheral target that had been flashed 1 to 30s before), controlled by the PEF, the FEF, the supplementary eye field (SEF), the DLPFC and the basal ganglia loop. Eye movements were recorded using EOG in 15 healthy adults at 3 different times: in the evening prior to SD (baseline), in the next morning following a one night's SD (day 1), and 24 hours later (day 2), following a night of sufficient sleep. A control group of 15 healthy adults was tested similarly, but without SD. Results showed specific effects of SD only on day 1, that had recovered completely on day 2 and were not found in the control group: 1) reduced peak velocities of all 3 types of saccades, indicating dysfunction of the paramedian pontine reticular formation (PPRF), which is part of the ascending reticular system involved in sleep-wake regulation; 2) prolonged latencies only of memory-guided saccades, but normal metrics, reflecting impaired initiation of voluntary saccades. Due to their long memorization times of up to 30s they had to be initiated almost like self-paced saccades which are controlled by the SEF. 3) Dysmetria (mainly hypometria) of visually-guided saccades, indicating rather a cerebellar dysfunction, as the essential functions of the PEF (latency of visually-guided saccades and metrics of memory-guided saccades) and of the FEF (error rate and latency of anti-saccades) were not affected. We conclude that sleep deprivation and reduced vigilance cause dysfunction of specific brain areas, such as the SEF, the cerebellum, and the PPRF, whereas other areas were not affected, particularly the primary frontal and parietal eye fields.

Sleep Deprivation: Effects on Pro-Saccades, Memory-Guided Saccades and Anti-Saccades

In this study we investigated the effect of sleep deprivation on different types of saccadic eye movements, namely reflexive visually-triggered saccades, memory-guided saccades and anti-saccades. These types of saccades differ in the extent of voluntary control and hence involve partially different brain structures. This study may reveal parameters and structures being most sensitive to sleep deprivation. Fifteen healthy volunteers participated in one adaptation night and one test night. During the test night half of the subjects (group 1) slept eight hours in a sleep laboratory, the other subjects (group 2) stayed awake. After four weeks the experiment was repeated with group 1 staying awake, group 2 sleeping. All subjects were tested in the evening before and in the morning after the test night (day 1). Furthermore all subjects were retested after one more night during which all were allowed to sleep (day 2). The tests consisted of a series of reflexive pro-saccades, anti-saccades and memory-guided saccades. Saccadic reaction time, peak velocity, and gain were computed for all saccades. Error rate was computed for the anti-saccade task. Before the test night and on day 2 there were no differences between sleep and sleep-deprivation conditions. All saccades showed a significantly reduced peak velocity on day 1 in the sleep deprivation condition. Surprisingly, pro-saccades had normal reaction times but reduced gain. Memory-guided saccades, however, did show prolonged reaction times with normal gain. Reaction times and gain of anti-saccades were not affected. Our data suggest that sleep deprivation does not provoke a general degradation of saccade parameters, but acts on certain parts of the saccadic network.

Eye movement and visuomotor arm movement deficits following mild closed head injury

THERE IS INCREASING EVIDENCE THAT EVEN MILD closed head injury (CHI) can cause considerable neural damage throughout the brain, in the form of either focal lesions or diffuse axonal injury. Indeed, a large proportion of mild CHI patients experience disabling persistent post-concussional complaints. At 6 months post-injury, approximately 30% of mild CHI patients meet the criteria for the diagnosis of post-concussion syndrome. None of the initial measures of trauma severity are able to predict the development of post-concussion syndrome. The authors hypothesized that mild CHI will disrupt the complex cerebral networks concerned with oculomotor and upper-limb visuomotor control, resulting in impaired motor function. They compared 30 patients with recent mild CHI (defined as Glasgow Coma Scale 13–15, alteration of consciousness <20 min, within 10 days of trauma) and 30 matched controls on different types of saccades, oculomotor smooth pursuit (sine and random), upper-limb visuomotor performance and several neuropsychological tests known to be sensitive to head trauma. Simple reflexive saccades were not impaired, whereas, on the antisaccade task, the CHI group demonstrated prolonged saccadic latencies, a marginally higher number of directional errors and poorer spatial accuracy. The CHI group exhibited more directional errors and impaired motor accuracy on memory-guided sequences of saccades and produced fewer self-paced saccades within 30 s. Most measures of sinusoidal and random oculomotor smooth pursuit showed no deficits, with the exception of a prolonged lag on random smooth pursuit in the CHI group. While arm movement reaction time and arm steadiness were not impaired, the CHI group showed decreased arm movement speed and decreased upper-limb motor accuracy. Conversely, after controlling for IQ, the CHI group had few head trauma-related neuropsychological deficits. These results indicate that multiple motor systems can be impaired following mild CHI and that this can occur independently of neuropsychological impairment. This study also indicates that quantitative tests of oculomotor and upper-limb visuomotor function may provide sensitive markers of cerebral dysfunction, suggesting the potential use of such tests to supplement patient assessment.—Valérie Biousse

Latency and accuracy of saccades to somatosensory targets

To examine the accuracy and latency of reflexive saccades to vibratory stimulation of the fingertips made by normal human subjects and to compare the findings to those of visually guided saccades. Eye movements were recorded using infrared oculography. Stimuli were presented via an array of audiometric bone vibrator transducers driven at 250 Hz and positioned at eye level in a darkened room. Target locations were at 0 and +/-5, 10, and 15 deg. Visual stimuli were green LEDs. Saccades were analysed interactively off-line and latency and amplitude measured for both types of saccade. Saccades to tactile stimuli had longer latencies and showed less accurate final eye positions than those to equivalent visual targets; they were unaffected by subject age. Error magnitude for the tactile saccades increased monotonically with increasing target eccentricity; because the fingers remained in a fixed position throughout the testing, this also meant that error was lowest for the thumb and increased with progression outwards towards the ring finger. Visually guided refixations were accurate and differed less than 0.2 deg across target locations. Subject age had no effect on performance. Human subjects may make relatively accurate refixations to tactile targets in the absence of visual cues, but only to certain locations/fingers; others were localised very poorly. Further studies are needed to determine whether finger selection or target location is the primary determinant of accuracy in this task.